I'm not big on chatting so I had tried MySpace and Facebook once, then quit them. Once I found out about the Facebook applications, though, I was hooked!
Which games do you play? Have you joined the forums of any games?
I used to play a bunch of games (Mafia Wars, Farm Town, Farmville, Heroes and Villains, Vampire Wars, Robin Hood, Space Wars, etc, etc), but now I only play Restaurant City and Frontierville. Both of those games suck up a lot of time so I couldn't keep up with my other applications. Plus, I was getting with bored with the other games and earning all kinds of in-game coins I could do nothing with.
I was very active in the Restaurant City forum and even organized some design contests. I stopped going there when I took a break from the game but have been going back recently. I don't hang out at the Frontierville forum but I do check in there once in a while when I'm having a problem in the game and want to see if other people are also reporting it. Frontierville is fun but it has more bugs than just about any other Facebook game I've played.
One more thing about applications: I used to like the send-a-round, pillow fights, poke and other apps but eventually I found them annoying and blocked them. I hardly have time to finish the missions in the few games I'm playing so I can't waste Facebook time on that kind of thing.